Method and device for producing workpieces by means of internal high pressure forming

ABSTRACT

A method for simultaneously producing at least two workpieces, separated from one another, by internal high pressure forming. A blank is inserted into a forming tool with at least two negative molds for each of the workpieces. There is at least one parting gap between each of the at least two respective negative molds and extending around each workpiece in the circumferential direction. Each parting gap defines two spaced-apart cutting edges. When the blank is acted upon by internal high pressure it comes into full contact with the forming tool inner wall. An especially simple construction is obtained for the forming tool if the cutting edges are exposed during the forming and if the blank, in the region of the at least one parting gap, penetrates into the latter during the forming, such that the cutting edges cut out a section between two respective workpieces.

This application is a national phase application of Internationalapplication PCT/EP2004/010106 filed Sep. 10, 2004 and claims thepriority of German application No. 103 50 154.1, filed Oct. 28, 2003,the disclosure of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method and a device forsimultaneously producing at least two workpieces, separated from oneanother, by means of internal high pressure forming or hydroforming.

The internal high pressure forming process, also called hydroforming, isbased on inserting a blank in the form of a hollow profile, for examplea tube, into a forming tool, in sealing off the blank on both sides andin applying an internal high pressure to it in such a way that the blanknestles against a negative mold, at a distance from it, of the formingtool and thus assumes the contours of said mold. In this way, hollowbodies can be produced which on the one hand may have a complicatedshape but on the other hand, at high strength, have a small wallthickness and thus a low weight. For reasons of economy, it is expedientto produce a plurality of workpieces simultaneously in one forming tool.

German patent document DE 197 16 816 C2 discloses a method and a deviceof the type mentioned at the beginning. Here, a blank is inserted into aforming tool which, with its inner wall, has at least two negative moldsfor in each case one of the workpieces and also at least one partinggap. This parting gap is arranged between two respective negative molds,extends all round in the circumferential direction of the workpieces andis defined by two spaced-apart cutting edges. Arranged in the respectiveparting gap in the known device is a tool part which can be positionedin the parting gap relative to the workpiece. To form the blank, thetool part is displaced toward the interior of the forming tool to suchan extent that an inner contour of the tool part terminates flush withthe cutting edges, so that the latter are sunk in the inner wall of theforming tool and are therefore inactive. The forming of the blank in theforming tool is effected with a calibrating pressure, which is selectedin such a way that the blank in the negative molds is in full contactwith the inner wall and therefore also with the inner contour of thetool part closing the parting gap. After this forming operation, aparting operation is effected, for which the pressure in the hollow bodyis increased above the calibrating pressure. Whereas the tool partarranged in the parting gap has still withstood the calibratingpressure, it is now displaced outward on account of the higher partingpressure. It is only by this relative adjustment of the tool part thatthe cutting edges are exposed, as a result of which a section arrangedbetween the cutting edges and therefore between the two workpieces iscut out.

The known device or the known method therefore works with two successivephases. In the first phase, the workpieces are shaped from the blank ina conventional manner, the workpieces still being in one piece with oneanother after the forming. In the subsequent second phase, by means ofan additionally increased internal pressure, the two workpieces are thenparted by releasing cutting edges.

The outlay for providing workpiece parts which withstand the calibratingpressure and do not release the cutting edges until at a higher partingpressure is relatively high in this case.

Furthermore, German patent document DE_(—)197 47 607 A1 discloses amethod and a device for perforating a workpiece, its one side beingsubjected to a pressure medium under high pressure and its other sidebeing subjected to the action of a punch guided in a tool, and thispunch releasing an encircling cutting edge which is formed on the tooland at which the wall is cut under the effect of an increasing highpressure.

The present invention deals with the problem of specifying an improvedembodiment for simultaneously producing at least two workpieces,separated from one another, by means of internal high pressure formingor hydroforming, which improved embodiment can be realized in particularin a more cost-effective manner.

The invention is based on the general idea of already arranging thecutting edges in an exposed manner during the forming of the blank andof carrying out the forming in such a way that the workpieces are partedat the same time. In the method according to the invention, therefore,the parting of the workpieces is integrated in the forming. In thiscase, the invention utilizes the surprising knowledge that a workpiecepart which closes the parting gap and produces a sunk arrangement of thecutting edges is not necessary for the forming of the blank. In theforming tool according to the invention, such tool parts for closing theparting gap are consequently dispensed with. This results in asimplified and more cost-effective construction for the forming tool.

According to an especially advantageous development, a gap width of theparting gap is dimensioned in such a way that the workpieces are partedat the calibrating pressure, at which the blank is in full contact withthe inner wall in the negative molds. With this proposal, the inventionin principle pursues a different way of designing the method parametersand the forming tool. In the conventional two-phase procedure, theparting gap is provided and dimensioned in the forming tool in such away that the desired parting of the at least two workpieces can thus becarried out with a corresponding increase in internal pressure. To thisend, the parting gap is closed by means of a suitable tool part forforming the blank. In this case, the holding forces for positioning theworkpiece part are selected as a function of the calibrating pressure,which is required for the proper forming of the blank, in such a waythat the workpiece part is not adjusted at the calibrating pressure andthe cutting edges cannot be exposed during the forming. For the partingoperation, such a high parting pressure is then selected that the toolpart can be displaced into the gap, the cutting edges can be exposed andthe desired section between the two shaped workpieces can be cut out. Incontrast to this, the gap width in the case of the invention is selectedas a function of the calibrating pressure, to be precise in such a waythat the section between the two workpieces is cut out at the same timeat the calibrating pressure. In the case of the invention, therefore,the parting gap is not dimensioned arbitrarily or as a function ofgeometrical constraints which result from the positioning of thenegative molds in the forming tool, but rather as a function of thecalibrating pressure. Accordingly, the positioning of the negative moldsinside the forming tool depends on the parting gap determined, and notthe other way round.

Since the workpieces are already parted at the calibrating pressure inthe method according to the invention, a two-stage method is dispensedwith, as a result of which the production overall is simplified.

The abovementioned features and the features still to be explained belowcan be used not only in the respectively specified combination but alsoin other combinations or on their own without departing from the scopeof the present invention.

A preferred exemplary embodiment of the invention is shown in thedrawings and is described in more detail below, the same referencenumerals relating to identical or functionally identical or similarcomponents.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingsfor example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show sectional views through a forming tool in accordancewith an embodiment of the present invention in the region of a partinggap in different states of a production process.

DETAILED DESCRIPTION

According to FIGS. 1 to 3, a forming and parting device 1 according tothe invention comprises a forming tool 2, which is only partly shownhere and has an inner wall 3, likewise only partly shown. Formed on orin this inner wall 3 are at least two negative molds 4 and 5, which eachserve to produce a workpiece 6 or 7, respectively, according to theinternal high pressure forming or hydroforming process. Formed in theinner wall 3 between two respective negative molds 4, 5 is a parting gap8 which extends all round in the circumferential direction of theworkpieces 6, 7. The parting gap 8 defines the two negative molds 4, 5and is in turn defined by two spaced-apart cutting edges 9 and 10. Inthis case, the cutting edges 9 and 10 define a gap width 11 of theparting gap 8.

According to the invention, the cutting edges 9, 10 are arranged in anexposed manner on the inner wall 3. That is to say that the parting gap8 is open and the cutting edges 9, 10 interrupt the inner wall 3 of theforming tool 2.

A blank 12, which normally has a hollow profile, can be inserted intothe forming tool 2.

In addition, the forming and parting device 1 according to the inventionhas a feed device (not shown here), by means of which a suitablepressure medium, expediently a liquid, in particular a hydraulic oil,can be delivered into the blank 12 and can be acted upon with anappropriate high pressure. Furthermore, in order to actuate and controlthe feed device, a corresponding control system (likewise not shown)which controls the sequence of the forming and parting operation isregularly provided.

The forming and parting method according to the invention or the formingand parting device 1 according to the invention works as follows:

First of all the blank 12 is inserted into the forming tool 2. The feeddevice at the blank 12 is then connected. After that, an internal highpressure can be built up in the blank 12 after the forming tool 2 hasbeen closed.

According to FIG. 2, the blank 12 is widened in the process, in thecourse of which a wall thickness 13 of the blank 12 naturally decreases.Here, FIG. 2 shows that instant or state of the forming and partingoperation at which or in which the blank 12 is widened to such an extentthat an outer contour 14 of the blank 12 comes into full surface contactwith the inner contours of the negative molds 4, 5. Full contact of theouter contour 14 of the blank 12 with the inner contours of the negativemolds 4, 5 is reliably achieved at a calibrating pressure P_(K). At thecalibrating pressure P_(K), the workpieces 6, 7 are therefore shaped inthe negative molds 4, 5. In the state according to FIG. 2, however, theshaped workpieces 6, 7 are still in one piece with one another or areconnected to one another via a section 15 arranged in between.

During the application of pressure to the blank 12, it may be expedientto constantly increase the internal high pressure to the calibratingpressure P_(K). It is important that the calibrating pressure P_(K) isproduced toward the end of the forming operation.

In a preferred embodiment of the present invention, the parting gap 8 ismatched to the calibrating pressure P_(K) in such a way that, at thecalibrating pressure P_(K), said section 14 is displaced according toFIG. 3 into the gap 8 and is accordingly cut free by the cutting edges9, 10. The section 15 is shaped so as to be closed all round, in acomplimentary manner to the parting gap 8. At the calibrating pressureP_(K), the section 15 arranged between the workpieces 6, 7 is cut out,which at the same time leads to parting of the two workpieces 6, 7. Theworkpieces 6, 7 then lie as separate, finish-formed components in theforming tool 2. In this embodiment of the method according to theinvention, a combined forming and parting operation is obtained for thesimultaneous production of at least the two workpieces 6, 7. Inparticular, it is not necessary to specifically raise the pressure forparting the workpieces 6, 7. As a result, firstly it becomes simpler tocarry out the forming/parting method and secondly the forming/partingdevice 1 has a simpler construction, so that it can be produced morecost-effectively.

For the design of the forming tool 2, first of all the calibratingpressure P_(K) which is required in order to bring the blank 12, withits outer side 14, into full contact with the negative molds 4, 5 isdetermined. When this calibrating pressure P_(K) is established, thewall thickness 13 remaining in the hollow profile after the forming isdetermined. The shearing force that is required for cutting off thesection 15 from the workpieces 6, 7 at the cutting edges 9, 10 can thenbe calculated from the residual wall thickness. By means of the shearingforce, the requisite gap width 11 at which the calibrating pressureP_(K) cuts out the section 15 can then be calculated with reference tothe calibrating pressure P_(K) and the predetermined circumference ofthe workpieces 6, 7 in the region of the parting gap 8. As soon as thegap width 11 of the parting gap 8 is established, the position of thenegative molds 4, 5 on both sides of the parting gap 8 in the formingtool 2 is thus obtained, provided the negative molds 4, 5 each start orend at one of the cutting edges 9, 10.

It may be necessary to vary the parting gap 8 over the circumference, sothat the cutting operation takes place as uniformly as possible.

In another embodiment, which is not preferred, the parting gap 8 mayalso be dimensioned in such a way that the calibrating pressure P_(K) isnot sufficient to drive the section 15 into the parting gap 8 or to cutthe section 15 out. For the parting operation, in this embodiment, theinternal high pressure is then correspondingly increased above thecalibrating pressure P_(K).

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1-2. (canceled)
 3. A method for simultaneously producing at least twoworkpieces, separated from one another, comprising the acts of:inserting a blank into a forming tool, the forming tool having in itsinner wall a negative mold for each of said at least two workpieces, andat least one parting gap which is arranged between two negative moldsand extends circumferentially around the workpieces, said parting gapdefined by two spaced-apart cutting edges; and applying an internal highpressure to the blank to form workpieces by deforming the blank toconform to an inner wall of each negative mold; wherein the cuttingedges are exposed such that they come into contact with the blank duringthe forming step, the blank enters the region of the at least oneparting gap and the cutting edges cut out a section between the at leasttwo workpieces, and a gap width of the parting gap is dimensioned suchthat the at least two workpieces are parted at a calibrating pressurewhich is above a pressure required to conform the blank to the innerwall of each negative mold.
 4. A device for simultaneously producing atleast two workpieces, separated from one another, by internal highpressure forming, comprising: a forming tool into which a blank can beinserted, wherein the forming tool includes in its inner wall a negativemold for each of said at least two workpieces and at least one partinggap which is arranged between two negative molds and extendscircumferentially around the workpieces, said parting gap defined by twospaced-apart cutting edges; a feed device for feeding a pressure mediuminto the blank inserted into the forming tool; and a control systemwhich activates the feed device to apply an internal high pressure tothe blank to form workpieces by deforming the blank to conform to aninner wall of each negative mold, wherein the cutting edges are arrangedsuch that they come into contact with the blank during the pressureforming, the at least one parting gap is arranged such that the blankenters the region of the at least one parting gap and the cutting edgescut out a section between the at least two workpieces, and a gap widthof the parting gap is dimensioned such that the at least two workpiecesare parted at a calibrating pressure applied by the feed device which isabove a pressure applied by the feed device to conform the blank to theinner wall of each negative mold.